The plan, which calls for airlines to collect fingerprints from aliens at the time of their departure from the U.S., follows the earlier implementation of the US-VISIT program, which takes fingerprints and photographs from aliens entering the U.S. The proposed exit system would allow immigration officials to match prints against those taken on entry to find out who has not left the U.S. on time.

Sales points out that Congress has called for exit controls since the 1990s and that many other countries have made successful use of such controls for years. Congress has a hard deadline of August 3, 2008, to establish a biometric exit system, based on 2007 legislation.

Excerpt:"The main value of exit is related to immigration" the ability to verify that guests don't overstay their welcome. Federal immigration officers can use exit data to track down violators who are still in the country and have them deported. Less direct enforcement is possible, too. State and local police can use exit data to check whether an alien pulled over for a traffic stop is out of status. And if border officials know a particular visitor previously overstayed, they can bar him from entering if he later tries to return to the U.S.

"While exit is largely about immigration, it also has national security-advantages. According to the 9/11 Commission, four of the September 11 hijackers — including Mohamed Atta, the plot's operational ringleader — had overstayed in the past. Hijacker Ziad Jarrah was an overstay when a Maryland state trooper gave him a speeding ticket just two days before the attacks. With an exit system, border officials could have turned away some of the hijackers when they subsequently tried to reenter the U.S. And police could have taken Jarrah into custody after a garden variety traffic stop.

"Why is DHS asking airlines to gather departure information on its behalf? The short answer is: Because they already do so. Right now, airlines are responsible for collecting biographic data about departing aliens — names, passport numbers, and the like — and transmitting it to DHS. The administration proposal simply adds another type of information to the list "fingerprints, a more reliable data point for matching entry and exit records.

"The longer answer is: Because there's no other way to run exit effectively. Taking fingerprints at the TSA security checkpoint would distract already overburdened screeners from their job of keeping weapons off planes. And allowing aliens to check out at out-of-the-way airport kiosks " which DHS tried in an early exit pilot "virtually guarantees low passenger compliance."